[sanitizer-common] Provide warning if task_set_exc_guard_behavior errors

Author: ndrewh

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

@@ -960,7 +960,18 @@ static void DisableMmapExcGuardExceptions() {
       RTLD_DEFAULT, "task_set_exc_guard_behavior");
   if (set_behavior == nullptr) return;
   const task_exc_guard_behavior_t task_exc_guard_none = 0;
-  set_behavior(mach_task_self(), task_exc_guard_none);
+  kern_return_t res = set_behavior(mach_task_self(), task_exc_guard_none);
+  if (res != KERN_SUCCESS) {
+    Report(
+        "WARN: AddressSanitizer: task_set_exc_guard_behavior returned %d (%s), "
+        "mmap may fail unexpectedly.\n",
+        res, mach_error_string(res));
+    if (res == KERN_DENIED) {
+      Report(
+          "HINT: Check that task_set_exc_guard_behavior is allowed by "
+          "sandbox.\n");
+    }
+  }
 }
 
 static void VerifyInterceptorsWorking();